An intervertebral prosthesis is implanted between two adjacent vertebrae in order to maintain or restore a space between the vertebrae while also preserving good mobility. An intersomatic cage is implanted between two adjacent vertebrae to allow the insertion and the growth of grafts of bony tissue (or a substitute) in the disc space, in order to achieve an arthrodesis (fusion of two vertebrae). After insertion of the cage, the intervertebral space may be filled with self-adapting spongy bone or suitable bony substitutes. The present invention concerns intervertebral prostheses and intersomatic cages for intervertebral fusion grafting and their attachment to the vertebrae by a bony anchoring device and their implantation in the disc space using implantation instruments.
A problem in this area concerns the stability of the intervertebral prostheses or of the intersomatic cages in the disc space after they have been implanted there, at least before the growth of the graft on either side of the cage and fusion with the vertebrae in the case of the intersomatic cages. For example, there exists a risk that the prosthesis or the cage will move within the intervertebral space under the effect of the stresses exerted upon it when the patient moves. The prosthesis or the cage must therefore not only have a shape that prevents it from pivoting but also have resources to prevent it from moving within the intervertebral space.
From previous designs, we know of solutions that consist of equipping the top and bottom surfaces of the prostheses or cages with notches so as to prevent movement. However, this type of solution is not perfect and the prosthesis or the cage still may move. We are also familiar, from previous designs, with solutions that consist of equipping the prosthesis or the cage with a bony anchoring device which is used to soundly attach the prosthesis or the cage to the vertebral plates of the vertebrae between which it is implanted. This type of bony anchoring device proves to be effective for securing the prosthesis or the cage. However, this type of solution presents problems during implantation.
Access to the intervertebral spaces is often particularly difficult because of the dimensions involved, and in particular due to the presence of blood vessels and nerves at the edges of the intervertebral space. The bony anchoring devices must penetrate into the vertebrae to a sufficient depth to secure the device. As a consequence, these bony anchoring devices are generally implanted along an approach axis that is more-or-less perpendicular to the plane of the intervertebral space or at least on a substantially oblique axis in relation to the plane of the intervertebral space. Other types of bony anchoring devices fit onto a plate that is substantially parallel to the axis of the vertebral column and extending the prosthesis or the cage on one of the faces of the vertebrae. These different types of device therefore require the surgeons to make large incisions, inducing prejudice and considerable risks for the patient. In addition, this type of bony anchoring device is not easy to implant since it requires that there is sufficient space at the edges of the intervertebral space to allow the implantation of the device, which unfortunately is not always the case, depending on the vertebrae in question.
In this context, it is useful to provide an anchoring device (which may be referenced below simply as a “device”) for an intersomatic cage or an intervertebral disc prosthesis that reduces the space at the edges of the intervertebral space that is necessary for the implantation of the cage itself, that makes the application of the anchoring device more convenient, or that provides better anchoring than some of the known anchoring means.